Vitamin D from sunlight

Published: Wednesday, September 26, 2007 at 4:30 a.m.

Last Modified: Wednesday, September 26, 2007 at 12:00 a.m.

Many seniors avoid being out in the sun. Some don't get outside much because they have difficulty getting out of their homes, while others find it uncomfortable to be out in the heat. Still more have been told by their doctors to protect their skin from further sun damage.

What they may not realize, however, that we all need a little sunlight on our skins to make vitamin D, which is vital for not only healthy bones but potentially to prevent a number of common cancers and other diseases. Recent studies have demonstrated that a large proportion of seniors in the U.S. (40 to 100 percent of those sampled in various studies) are vitamin D deficient. The next two columns will cover why this deficiency is important, and some simple steps to prevent or correct the problem.

Humans get vitamin D from exposure to sunlight, from their diets, and from supplements. A component of sunlight (ultraviolet B radiation or UVB), is responsible for converting a precursor chemical called 7-dehydrocholesterol to pre-vitamin D3 which is rapidly converted into the active form of vitamin D (D3). Interestingly, because D3 is also broken down by sunlight, getting more sunlight doesn't lead to too much vitamin D.

The amount of time in sunlight required to get enough UVB to produce sufficient vitamin D for optimal health can vary considerably by how light or dark your skin is (darker skin blocks more UVB than light skin), how much skin you have exposed to sunlight, and the season, latitude, and time of day you are outside (when the sun is lower in the sky our atmosphere blocks more UVB light).

As a rule of thumb in this area, however, exposing your arms and legs to about 5 to 10 minutes of mid-day summer sun or 30 minutes of winter sun at least twice a week is sufficient to keep vitamin D levels in a good range.

Diet is another source of vitamin D. Eating a diet that is rich in oily fish such as cod or salmon can prevent vitamin D deficiency, but very few people actually eat near enough fish to have this beneficial effect. Some foods in the U.S. are routinely fortified with vitamin D, such as milk, and many seniors take a daily multivitamin (such as Centrum Silver) which frequently have up to 400 IU (international units) of vitamin D.

Nevertheless, despite these other sources of vitamin D, deficiency is quite common, as noted above. In fact, one study of medical students, residents and physicians in a Boston hospital found that despite reporting eating fish at least once a week, drinking at least one glass of milk a day, and taking a daily multivitamin that nearly one third of these health professionals had vitamin D deficiency. Obviously, these doctors didn't go outside much!

One of the most important functions of vitamin D is that it dramatically improves the absorption of calcium and phosphorus from the food we eat. With low levels of vitamin D we absorb only about 10 to 15 percent of ingested calcium, and 60 percent of ingested phosphorus; this absorption increase to 30 to 40 percent and 80 percent, respectively, when vitamin D is present in sufficient quantities.

Calcium and phosphorus are critical building blocks for strong, healthy bones, and a number of recent studies demonstrate that sufficient levels of vitamin D can reduce the risk of hip fractures in the elderly by as much as 40 percent over a three year period.

Because nearly 50 percent of women and 22 percent of men over 50 will experience a fracture due to thin bones during their remaining years of life, and because these fractures are among the leading causes of seniors losing their ability to live independently, preventing these fractures is of great importance.

The amount of supplementation needed, however, is about twice what is currently contained in most multivitamins. Studies using 400 IU of vitamin D every day did not show a significant reduction in fractures, but those with 700-800 IU a day showed at 25 to 32 percent reduction in the hip fracture rate.

Next month we will discuss other possible benefits of vitamin D, how to know if you are deficient, and some simple strategies to correct this common problem.

<p>Many seniors avoid being out in the sun. Some don't get outside much because they have difficulty getting out of their homes, while others find it uncomfortable to be out in the heat. Still more have been told by their doctors to protect their skin from further sun damage. </p><p>What they may not realize, however, that we all need a little sunlight on our skins to make vitamin D, which is vital for not only healthy bones but potentially to prevent a number of common cancers and other diseases. Recent studies have demonstrated that a large proportion of seniors in the U.S. (40 to 100 percent of those sampled in various studies) are vitamin D deficient. The next two columns will cover why this deficiency is important, and some simple steps to prevent or correct the problem.</p><p>Humans get vitamin D from exposure to sunlight, from their diets, and from supplements. A component of sunlight (ultraviolet B radiation or UVB), is responsible for converting a precursor chemical called 7-dehydrocholesterol to pre-vitamin D3 which is rapidly converted into the active form of vitamin D (D3). Interestingly, because D3 is also broken down by sunlight, getting more sunlight doesn't lead to too much vitamin D. </p><p>The amount of time in sunlight required to get enough UVB to produce sufficient vitamin D for optimal health can vary considerably by how light or dark your skin is (darker skin blocks more UVB than light skin), how much skin you have exposed to sunlight, and the season, latitude, and time of day you are outside (when the sun is lower in the sky our atmosphere blocks more UVB light).</p><p>As a rule of thumb in this area, however, exposing your arms and legs to about 5 to 10 minutes of mid-day summer sun or 30 minutes of winter sun at least twice a week is sufficient to keep vitamin D levels in a good range.</p><p>Diet is another source of vitamin D. Eating a diet that is rich in oily fish such as cod or salmon can prevent vitamin D deficiency, but very few people actually eat near enough fish to have this beneficial effect. Some foods in the U.S. are routinely fortified with vitamin D, such as milk, and many seniors take a daily multivitamin (such as Centrum Silver) which frequently have up to 400 IU (international units) of vitamin D. </p><p>Nevertheless, despite these other sources of vitamin D, deficiency is quite common, as noted above. In fact, one study of medical students, residents and physicians in a Boston hospital found that despite reporting eating fish at least once a week, drinking at least one glass of milk a day, and taking a daily multivitamin that nearly one third of these health professionals had vitamin D deficiency. Obviously, these doctors didn't go outside much!</p><p>One of the most important functions of vitamin D is that it dramatically improves the absorption of calcium and phosphorus from the food we eat. With low levels of vitamin D we absorb only about 10 to 15 percent of ingested calcium, and 60 percent of ingested phosphorus; this absorption increase to 30 to 40 percent and 80 percent, respectively, when vitamin D is present in sufficient quantities. </p><p>Calcium and phosphorus are critical building blocks for strong, healthy bones, and a number of recent studies demonstrate that sufficient levels of vitamin D can reduce the risk of hip fractures in the elderly by as much as 40 percent over a three year period. </p><p>Because nearly 50 percent of women and 22 percent of men over 50 will experience a fracture due to thin bones during their remaining years of life, and because these fractures are among the leading causes of seniors losing their ability to live independently, preventing these fractures is of great importance.</p><p>The amount of supplementation needed, however, is about twice what is currently contained in most multivitamins. Studies using 400 IU of vitamin D every day did not show a significant reduction in fractures, but those with 700-800 IU a day showed at 25 to 32 percent reduction in the hip fracture rate.</p><p>Next month we will discuss other possible benefits of vitamin D, how to know if you are deficient, and some simple strategies to correct this common problem.</p>